1. Field of Invention
The present invention relates to a display apparatus. More particularly, the present invention relates to a display apparatus in which an electric power is supplied to a light source unit by a switching method.
2. Description of the Related Art
A light emitting diode (LED) has been used as a light source in a display apparatus instead of a cold cathode fluorescent lamp (CCFL) to improve color reproducibility. The display apparatus using the LED is improved in the color reproducibility.
A conventional display apparatus comprising an LED light source controls the LED light source using either a linear method or a switching method.
In the linear method, the display apparatus comprises a constant voltage source for generating voltage to be provided to the LED light source, a switching unit for switching so that an electric current by the voltage from the constant voltage source flows to the LED light source, and a pulse width modulation (PWM) generator for turning on/off the switching unit. According to the linear method, noise and ripple is slight while the LED light source should be constantly supplied with a work current of a linear region. Therefore, when the LED light source has a high load of current, voltage loss generated in the switching unit grows high to continuously provide the work current of the linear region.
In the switching method, the display apparatus comprises a constant current source generating current to be provided to the LED light source, a switching unit for switching so that the current from the constant current source flows to the LED light source, and a PWM generator for turning on/off the switching unit. The work current flows to the LED light source in a PWM-on section to turn on the LED light source, and a “0” current flows to the LED light source in a PWM-off section to turn off the LED light source. Here, the switching unit is turned on/off according to the amount of the current flowing in the LED light source in the PWM-on section, the amount of the current flowing in the LED light source pulsates slightly and an average work current flows in the LED light source.
In the switching method, ripple is generated in a cycle corresponding to switching on/off while the current is provided to the LED light source, and accordingly a light characteristic of the LED light source is deteriorated. An inductor with high capacity may be used or a switching frequency may be raised to remove the ripple. However, the inductor with high capacity is not easily manufactured, and its characteristics deteriorates as its volume increases. Further, switching loss increases as the switching frequency is raised, thereby efficiency of the display apparatus is reduced.
Accordingly, there is a need for an improved system and method for providing a display apparatus in which a current ripple is decreased to improve characteristics of a display apparatus.